Position tracking system

ABSTRACT

An optical position tracking system that tracks the position of objects, using light intensity and/or frequency with the application of geometry and ratios of detector responses, is provided, having light distributing and light detecting components that employ the concepts of constructive occlusion and diffuse reflection. Diffusely reflective cavities, masks and baffles are used to improve certain radiating characteristics of the distributing components and certain response characteristics of the detecting components, to tailor the radiation and detection profiles thereof, including them substantially uniform for all angles within a hemispheric area which the distributing and detecting components face. The distributing and/or detecting components are partitioned with specially-configured baffles. A partitioned distributor has distinct emission sections where the sections can emit spectrally-different or distinguishable radiation. A partitioned detector has distinct detection sections where the sections can detect radiation from different directions. The system may be variously configured, to use different combinations of partitioned and nonpartitioned devices. In most configurations, a single head module provides one set of directional data about two coordinates (e.g., ρ and Θ) for one reflector. An additional head module remotely positioned from the first head module can provide a second set of directional data for the reflector (e.g., ρ 2  and Θ 2 ), for cross-referencing with the first set of directional data to obtain positional data in three dimensions of the object being tracked. The system can also track multiple objects, using spectrally-different (or at least spectrally distinguishable reflectors) in conjunction with correspondingly spectrally-compatible sensors to distinguish between data collected for each reflector. Numerous variations particularly on the concept of constructive occlusion may be accomplished with varying results as desired or appropriate. By reconfiguring the radiation/detection surface, the cavity, the mask and/or the baffle, the radiation/detection profile may be varied in substantially unlimited ways.

This application is a continuation of application Ser. No. 08/781,826filed Jan. 10, 1997 now U.S. Pat. No. 6,043,873.

BACKGROUND OF THE INVENTION

The present invention relates generally to optical emitters anddetectors, and optical position tracking devices, in particular, opticaldevices having distinct radiation and detection properties that may beused to track position of objects, using a relatively small number ofoptical elements.

Position tracking is a growing technology with ever increasingapplications. For example, in the entertainment arena, position trackingin three dimensions is used in virtual reality simulation. Positiontracking is also used in the industrial arena, with applications inprocess control and robotics. The field of biomedics also uses positiontracking devices for tracking portions of a human body to determine thebody's motion patterns. Similarly in animation dynamics, the tracking ofmultiple body parts is used for controlling animated figures. Many otherapplications exist, for which position tracking is useful if notadvantageous.

Conventional position tracking can be broken down into two broadtechnologies, i.e., active systems and passive systems. Active systemsutilize active electronic elements on the objects being tracked. Forexample, the Polhemus' 3SPACE ISOTRACK II® system uses active magneticelements to create a dynamic magnetic field that is representative ofthe body's position. By sensing changes in the magnetic field, thesystem delivers all six axes of the object's spatial location.

Active systems are generally high-performance, high-end products.However, they can have disadvantages, including limited range of motion,metal interference, complex operation and high cost. In particular, therange of the magnetic field is typically limited, and trailingconnection wires are often a nuisance. Where the area of motion containssubstantial metal, mapping of the entire field is usually part of thesystem's required initialization.

In contrast, passive systems track objects without physical linksbetween the object and the system. Target points such as retroreflectors may be used, or image processing of a video image may beperformed. While passive systems are often less complex and lessexpensive compared to active systems, they are often lacking inresolution. Thus, for object recognition, passive systems typicallyrequire extensive image processing, which can increase costs and theprobability of errors. The use of reflectors avoids some of theseproblems, but not without introducing other problems, such as the needfor critical alignment and extensive initialization.

Aside from the various system limitations discussed above, the sensingcomponents of an optical detector, such as photodiodes or charge-coupleddevice (CCD), have their own limitations. While these components can bemade directionally-sensitive (e.g., with the provision of a slit, or theuse of Gray-coded multi-element arrays), the response is often limited.For example, they typically provide directional information orresolution about one axis only, and the sensor's accuracy is typicallylimited by the number of optical elements provided.

It should therefore be appreciated that there exists a definite need fora relatively simple and inexpensive position tracking system, which cantrack the position of an object along at least three axes, if not allsix axes to include objection rotation, using minimal electrical and/oroptical elements. It is desired that the system has low alignment andinitialization requirements and low processing demands. In that regard,it is desired that the system be structurally and electronically simple,while remaining capable of providing at least directional indicative ofthe direction along which the object is positioned relative to thesystem. It is further desired that the system be able to providelocational data inclusive of range data, along with directional data,for tracking an object in three dimensional space. The present inventionaddresses all of these desires and more.

SUMMARY OF THE INVENTION

The present invention resides generally in an optical position trackingsystem that tracks the position of objects, using light intensity and/orfrequency with the application of geometry and ratios of detectorresponses.

The present invention provides for the illumination of an area that maybe defined by spherical or hemispherical coordinates with a tailoredspatial intensity profile, and/or the detection of light associated withan object in the area, with the recognition that certain characteristicsor properties of the light detected are indicative of the relativeposition or movement of the object in the area. Advantageously, theinvention applies the concepts of constructed occlusion and diffusereflection to accomplish its purpose with improved efficiency.

The positioning tracking system in one embodiment includes a retroreflector that is affixed to the object being tracked, and a head modulethat includes a light distributor and a light detector. Constructedocclusion as employed by the present invention includes the use of amask that improves certain radiating characteristics of the distributorand certain response characteristics of the detector. For example, amask in a predetermined position enables the distributor to provide amore uniform radiation profile, and the detector to provide a moreuniform response profile, at least for elevations approaching thehorizon. In general, changing the position and/or size of the maskchanges the radiating and response profiles. The profiles may be furthermanipulated or enhanced with the use of a baffle, particular for theprofile at angles at or near the horizon. The baffle can be conical oran intersecting structure. Where the electromagnetic radiation utilizedby the present invention includes visible light, components includingthe mask and the baffle are formed of a Lambertian, polymeric materialhaving a reflectance of approximately 99% for visible wavelengths.

In accordance with a feature of the present invention, the distributionprofile of a constructively occluded distributor can be specificallytailored or made substantially uniform for over most, if not all,azimuths and elevations of a hemispheric area over the distributor.Correspondingly, the response profile of a constructively occludeddetector can be specifically tailored or made substantially uniform formost, if not all, azimuths and elevations of a hemispheric area over thedetector. In essence, constructed occlusion can render both thedistributor and detector uniformly omnidirectional in the hemisphericarea which the occluded device faces.

In order that the system track the position of a reflector (or point),or at least provide directional information for that reflector, the headmodule of the system includes a partitioned occluded device which may beeither the distributor or the detector. In particular, the use of apartitioning baffle in a distributor renders a partitioned distributorhaving distinct emission sections where the sections can emitspectrally-different or distinguishable radiation. Correspondingly, theuse of a partitioning baffle in the detector renders a partitioneddetector having distinct detection sections where the sections candetect radiation from different directions.

The system may be variously configured, to use different combinations ofpartitioned and nonpartitioned devices, that is, a partitioneddistributor with a nonpartitioned detector, or a nonpartitioneddistributor with a partitioned detector. A partitioned distributorprovides a plurality of radiation sections and a partitioned detectorprovides a plurality of detection sections. In most configurations, asingle head module provides one set of directional data about twocoordinates (e.g., ρ and Θ) for one reflector, using one of thesecombinations, wherein one of the devices is partitioned into foursections or quadrants.

An additional head module remotely positioned from the first head modulecan provide a second set of directional data for the reflector (e.g., ρ₂and Θ₂). By cross-referencing the second set of directional data withthe first set of directional data, the system is able to obtainpositional data in three dimensions of the reflector, that is, threecoordinates, along three axes for the reflector.

The system can also track additional reflectors, usingspectrally-different (or at least spectrally distinguishable reflectors)in conjunction with correspondingly spectrally-compatible sensors todistinguish between data collected for each reflector. Where the systemuses a head module having a nonpartitioned distributor and a partitioneddetector to detect one reflector, the system can use additional headmodules, each housing an additional set of sensors corresponding to anadditional reflector. However, the system can also use a single headmodule that is configured to house all of the additional sets ofsensors. In particular, the single head module can be configured havingone partitioned detector where each section houses a sensor from a setcorresponding to a reflector being tracked. Accordingly, a single headmodule can track multiple reflectors.

As variations on the head module described above, the nonpartitioneddistributor and the partitioned detector may use separate cavities orshare a single cavity within the head module. Moreover, as furthervariations, the nonpartitioned distributor of the head module may emitcontinuous broad band radiation or pulses of broad band radiation. Wherethe radiation is emitted in pulses, the elapsed time for the pulseradiation to reflect off the reflector can be analyzed by the system asdata providing a range coordinate for the tracked reflector. Using boththe intensity variation of the radiation, and the elapse time of thepulses, the system can derive all three coordinates for a reflector,without using a separate head module.

Because the system illuminates the detection zone without discriminatingbetween the object being tracked and any other extraneous objects, suchas furniture or walls, background or self illumination can besignificant and adversely affect the system's performance. Where sensorsof different or distinguishable spectral characteristics are used in thesystem for detecting multiple reflectors, the system provides a separateset of sensors dedicated to sensing background illumination so that theeffects of self illumination can be compensated.

The system may also be configured to reduce the level of backgroundillumination. In particular, the system utilizes a head module having ascanning beam source that is situated between a split partitioneddetector. The beam is of a predetermined width and sweeps the detectionzone in search of reflectors. With the beam illuminating only a portionof zone at any give time, background illumination is substantiallyreduced and the system is therefore available to perform a coloranalysis using a relatively small number of filter sensor combinationsto distinguish between a very large numbers ofspectrally-distinguishable reflectors. Like the previous embodiments,this embodiment uses two head modules to detect all three coordinates ofone reflector.

In an alternative embodiment also using color analysis, the system usesa head module that includes a nonpartitioned detector with a partitioneddistributor. The partitioned distributor houses in each section a lampof a distinguishable color (frequency), such that each section isdistinctly associated with a distinguishable color. In accordance withthe application of color analysis, the detector houses a smallcombination of filtered sensors. The color mix reflected by a reflectoris analyzed by the system to indicate a set of directional data for thereflector relative to the head module.

The system may also be configured as an optically active system, usingactive light sources, such as LEDs, that are placed on the object beingtracked, and a partitioned detector. In this embodiment, light emittedfrom the LEDs are detected by the partitioned detector, and the color oroscillation frequencies of the LEDs are used to distinguish betweendifferent LEDs.

Other optical devices and position tracking systems are contemplated bythe present invention. For example, an optical device configured as aring having two structures which selectively occludes the opticalsurface of the other for different elevation angles is provided. Again,the principles of constructed occlusion is applied such that the devicehas a tailored or substantially uniform profile which can render thedevice hemispherical as a radiator or a detector. To also render thedevice directional, the structure may be configured such to providedistinct and separate segments.

Other features and advantages of the present invention should becomeapparent from the following description of the preferred embodiments,taken in conjunction with the accompanying drawings, which illustrate,by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a position tracking system, inaccordance with the present invention, for determining and displayingthe position of game equipment;

FIG. 2 is a schematic diagram of a Lambertian surface, demonstrating thecosine dependence property associated therewith;

FIGS. 3A and 3B are schematic diagrams of a mask used to constructivelyocclude a Lambertian surface;

FIG. 4 is a side cross-section view of an optical arrangement employingthe concepts of constructive occlusion and diffusive reflection, inaccordance with the present invention;

FIG. 5 is a graph illustrating the cosine dependence of the arrangementof FIG. 4;

FIG. 6 is a side cross-section view of an optical arrangement employingthe concepts of constructive occlusion and diffusive reflection, and aconical baffle, in accordance with the present invention;

FIG. 7 is a graph illustrating the substantial alleviation or treatmentof the cosine dependence of the arrangement of FIG. 6;

FIGS. 8A and 8B are perspective views of an intersecting baffle, inaccordance with the present invention;

FIG. 9 is a perspective view of another intersecting baffle, inaccordance with the present invention;

FIG. 10 is a side cross-section view of an optical arrangement employingthe concepts of constructive occlusion and diffuse reflection, and theintersecting baffle, with treatment of the Fresnel reflection, inaccordance with the present invention;

FIG. 11 is a side cross-section view of an optical arrangement with aspecially configured mask having properties of a baffle;

FIG. 12A is a side cross-section view representative of a partitioneddistributor and a partitioned detector, in accordance with the presentinvention;

FIG. 12B is a cross section view of FIG. 12A, taken along line B—B.

FIG. 13 is a perspective view of a head module used in association withan oscilloscope, in accordance with the present invention;

FIG. 14 is a conceptual representation of X-Y coordinates of a displayof the oscilloscope of FIG. 13;

FIG. 15 is a schematic diagram of the electronics for convertingelectrical signal from the head module of FIG. 13, to the X-Ycoordinates of the oscilloscope of FIG. 13;

FIG. 16 is a side cross-section view of an embodiment of the headmodule, in accordance with the present invention;

FIG. 17 is a cross-section view of FIG. 16, taken along line X—X;

FIG. 18A is a side cross-section view of another embodiment of the headmodule, in accordance with the present invention;

FIG. 18B is a cross-section view of FIG. 18A taken along line B—B;

FIG. 19A is a side cross-section view of a further embodiment of thehead module, in accordance with the present invention;

FIG. 19B is a cross-section view of FIG. 19A, taken along line B—B;

FIG. 20A is a side cross-section view of yet another embodiment of thehead module, in accordance with the present invention;

FIG. 20B is a cross-section view of FIG. 20A, taken along line B—B;

FIG. 21 is a perspective view of another embodiment of the system, inaccordance with the present invention;

FIG. 22A is a plan view of a platform on which four individualpartitioned detectors are mounted;

FIG. 22B is a side view of the platform of FIG. 22A;

FIG. 23A is a top plan view of another embodiment of an occluded devicein accordance with the present invention;

FIG. 23B is a side view of the occluded device of FIG. 23A;

FIG. 23C is a side view rotate 90 degrees from the view of FIG. 23B;

FIG. 24A is a perspective view of a ring detector in accordance with thepresent invention;

FIG. 24B is a top plan view of the ring detector of FIG. 24A;

FIG. 24C is a cross section view of the ring detector of FIG. 24A,demonstrating the substantially constant cross section area providedthereby;

FIG. 25A is a perspective view of a sectioned ring detector inaccordance with the present invention;

FIG. 25B is a top plan view of the ring detector of FIG. 25A;

FIG. 25C is a side view of the ring detector of FIG. 25A, demonstratingthe substantially constant cross section area provided thereby;

FIG. 26A is a top plan view of a multiple cavitied optical device inaccordance with the present invention;

FIG. 26B is a side cross-section view of the device of FIG. 26A, takenalong line B—B;

FIG. 27A is a side cross-section view of another embodiment of anoptical arrangement employing the concepts of constructive occlusion anddiffusive reflection, and a baffle, in accordance with the presentinvention;

FIG. 27B is a view of the optical arrangement of FIG. 27A taken alongline B—B;

FIG. 28 is a side cross-section view of two partitioned opticalarrangements configured back-to-back to provide spherical coverage inaccordance with a feature of the present invention;

FIG. 29A is a perspective view of two sectioned ring detectorsconfigured back-to-back to provide spherical coverage in accordance withthe present invention;

FIG. 29B is a side cross section view of the ring detectors of FIG. 29A;

FIG. 30A is a side cross section view of one embodiment of an azimuthaldevice in accordance with the present invention;

FIG. 30B is a view of the azimuthal device of FIG. 30A taken along lineB—B;

FIG. 30C is a view of the azimuthal device of FIG. 30A taken along lineB—B, with a tailored coverage;

FIG. 31A is a side cross section view of another embodiment of theazimuthal device in accordance with the present invention;

FIG. 31B is a view of the azimuthal device of FIG. 31A taken along lineB—B; and

FIG. 31C is a view of the azimuthal device of FIG. 31A taken along lineB—B, with a tailored coverage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the exemplary drawings, the present invention resides in anoptical position tracking system 10 that tracks the position of anobject, without requiring complicated electrical wiring, expensivephotodetector arrays, video cameras, or image processing. Morespecifically, the system measures optical properties such as lightintensity and frequency to provide at least directional data along twoaxes, if not positional data along three axes, for the object beingtracked. If desired, the system may also provide positional androtational data along six axes for the object being tracked.

Referring to FIG. 1, the position tracking system has numerousapplications. For example, the system may be used in a video game 11,where signals representative of the position or movement of gameequipment within a zone Z are detected and processed, and converted tovideo signals fed to a video monitor. Though the system and display 15are shown outside the zone Z, these components may of course be insidethe zone Z.

One embodiment of the position tracking system 10 is shown in FIG. 1,having a head module H tracking a retro reflector RR1. In accordancewith a feature of the invention, the head module H utilizes the conceptsof constructed occlusion and diffuse reflection, both of which arediscussed below in further detail.

As background, constructed occlusion may be used to change certaincharacteristics of a substantially Lambertian surface, whether it is anemitter or a detector surface. A substantially Lambertian emitter X isshown in FIG. 2. While the emitter X is illustrated with a planarsurface, an emitter surface with substantially Lambertian propertiesneed not be planar.

It is observed that the radiation intensity of the emitter X varies withthe angle φ. Thus the emitter X has a radiation intensity profile thatis a function of the angle φ. This function or relationship between theradiation intensity and the angle φ can be seen in the change in thecross sectional area K of the surface A as the angle φ changes. Inparticular, where φ is defined from the normal of the emitter surface A,the cross sectional area K varies as a cosine function of the angle φ.

FIG. 2 is also representative of a substantially Lambertian detector(also designated by X). While the detector X is shown with a planarsurface, a detector surface with substantially Lambertian propertiesneed not be planar. As the emitter X, the detector X has a responseintensity profile that is a function of the angle φ. Again, thisfunction can be seen in the change in the cross section area K, whichdecreases as the angle φ increases from the normal to the horizon.

Constructed occlusion aims to reduce, if not eliminate, the cosinedependency on the angle φ in both the emitter X and the detector X. Asshown in FIGS. 3A and 3B, a mask M is employed to constructively occludethe surface A. Properly sized and positioned from the surface A, themask M is rendered to selectively “block” portions of the surface A,such that the cross section area K remains constant for most angles ofφ. Accordingly, the mask M offsets the change in cross section area Ksuch that the radiation or response profile of the surface issubstantially uniform for angles of φ, except those near the horizon.For the configuration shown in FIGS. 3A and 3B, the cross section area Kremains constant for angles of φ between 0 and approximately 80 degrees.This range of angles varies with different geometry between the mask,aperture and cavity. Overall, the radiation or response profile may bedistinctly manipulated as desired with different mask and surfacegeometry.

While the mask M may be completely opaque, constructive occlusion may beachieved without complete opacity in the mask M. So long as the mask Mprovides a relative reduction in the transmission of radiation betweenoccluded and nonoccluded areas, the cosine dependence is altered.

As mentioned, the system also applies the concept of diffuse reflection.As background, a diffusive reflector can increase the efficiency of anoptical system by allowing a surface emitter or detector to be replacedby a point emitter or detector. For both cases, reference is made toFIG. 4.

A substantially Lambertian emitting surface LS can be created using apoint illuminating element 12 (such as a fiber optic) that illuminates acavity 16 whose interior surface 20 is diffusely reflective. The cavity16 diffusely reflects radiation from the point element 12 such that auniformly illuminated surface 21 is created at the aperture 22 of thecavity 16. Correspondingly, a substantially Lambertian detection surfaceLS can be created using a point detecting element 12 (such as aphotodiode) that detects light within a cavity 16 whose interior surface20 is diffusely reflective. The cavity 16 diffusely reflects radiationentering the cavity 16 through the aperture 22 such that the pointdetecting element 12 uniformly detects radiation reaching the aperture22. It is understood by one of ordinary skill in the art that the pointelement 12 may be a device localized at the cavity 16, or alight-conveying device, such as a fiber optic 14 or an opticalwaveguide, that efficiently transmits light into or away from the cavity16 to another area.

With selective placement and/or sizing of the mask M above the aperture22, the occluded arrangement of FIG. 4 can either (i) illuminate an areaoven the aperture 22 with an intensity profile that is substantiallyuniform in almost all directions of the area, as an occludeddistributor, or (ii) uniformly detect radiation over almost alldirections of the area, as an occluded distributor, where the area isreadily defined in rho and theta directions in spherical orhemispherical coordinates. The radiation and detection profiles canremain substantially uniform for most angles in accordance with theselected mask/cavity/aperture geometry, except for those angles at ornear the horizon of the occluded arrangement (hereinafter referred to asthe horizon district).

The cavity 16 of FIG. 4 can be provided in a base 18 which also providesa shoulder 28 surrounding the aperture 22 of the cavity. The base 18 maybe formed of aluminum, plastic, or like materials, and covered with acoating of diffusely reflective substance, such as barium sulfate, sothat the base 18 as a whole can diffusely reflect incident light. Thebase 18 may also be formed of a diffusely reflective bulk material suchas Spectralon® sold by Labsphere Inc., of North Sutton, N.H. Spectralon®is easily machined, durable, and provides a highly efficient Lambertiansurface having a reflectivity of over 99%, in visible and near-infraredwavelengths. Other suitable materials, though typically less effectivethan the diffuse reflective materials mentioned above, includequasi-diffuse reflective materials, such as flat white paint.

The mask M, in particular its underside 24, is also constructed of adiffusely reflective material, such as Spectralon®, so that any lightincident on the underside of the mask M is not lost but reflected backinto the cavity 16. The light redirected back into the cavity 16 is, onaverage, reflected many times within the cavity 16 and adjacentdiffusely reflective components.

The cavity 16 is illustrated as a hemispherical cavity; however, thecavity may be any shape. Moreover, the size of the aperture 22 need notbe comparable to the maximum cross-sectional area of the cavity; thatis, the cavity may be more spherical than hemispherical. Furthermore,the aperture 22 need not be planar. However, the hemispherical cavitywith a planar aperture may be preferred as it is easier to construct andit affords geometric symmetries that allow the use of simplifyingcalculations and assumptions.

Where the cavity 16 is hemispherical (or spherical) and the aperture 22planar, as shown in FIG. 4, the aperture 22 of the cavity 16 defines adiameter D_(a) and the mask defines a diameter D_(M). As mentioned, theratio between the diameters D_(a) and D_(M) is a parameter that canchange the profile (radiation or response) over the entire 2π steradianhemisphere which the occluded arrangement faces. In general, uniformityin the profile is increased if the mask/cavity diameter ratio is closeto one; however, this ratio reduces the efficiency of the occludedarrangement by diminishing the acceptance/escape area between the maskand the aperture. It is currently believed that by decreasing theintensity for certain angles while increasing the intensity for otherangles, the mask substantially averages the profile over a wide range ofangles, for a more uniform efficiency for most angles. A mask/cavitydiameter ratio of about 0.8 to 0.9 is preferred. This ratio provides areasonably level profile, while maintaining a relatively high level ofefficiency.

The distance or height D between the mask M and the aperture 22 isanother parameter that can change the occluded arrangement's radiationor detection profile. Moreover, the thickness of the mask M can alsochange the profile.

The graph of FIG. 5 shows the cross-sectional area K of an occludedarrangement with an aperture diameter of approximately 2.0″, a mask witha diameter of approximately 1.8″, and a separation distance between themask and aperture of approximately 0.3″. It can be seen that the profileof this occluded arrangement remains relatively constant until φ reachesapproximately 80 degrees. Thereafter the profile drops dramatically.

As different profiles may be obtained with differentmask/cavity/aperture geometry, it may be useful to construct the cavityand mask out of a core material that is pliant, e.g., rubber, so thatthe cavity and/or mask may be readily reconfigured to provide differentgeometries with different radiation or detection profiles.

In order to expand the uniform portion of the profile into greaterangles of φ, that is, into the horizon district, the system 10 mayeither increase the energy of the illumination radiated or detected, orprovide a deflector or baffle 30 as shown in FIG. 6. The baffle 30 isconfigured to provide a surface 32 below the mask M, that issubstantially perpendicular to the horizon district. The surface 32serves to reflect light to the horizon district to significantlyincrease the illumination intensity in that district. Like the mask Mand the base 18, the baffle 30 is constructed out of a diffuselyreflective material such as Spectralon®. The reflectivity of the bafflescan be graded so that the baffle can have an angle dependentreflectivity, if desired, for example, to compensate nonuniform effects.

Used appropriately, the baffle 30, in conjunction with the shoulder 28,can extend the profile uniformity into angles of φ well beyond 90degrees (see, e.g., FIG. 7). For an occluded emitter arrangement, theshoulder 28 redirects toward the upper hemispheric area that wouldotherwise be directed below the horizon. For an occluded detectorarrangement, the shoulder 28 blocks light from below the horizon.

As mentioned, the radiation or detection profile over the hemisphericarea may be tailored as desired by carefully configuring anddimensioning the cavity aperture 22, the mask M, the baffle 30, and/orthe shoulder 28. For example, referring to FIG. 7, an occludeddistributor R having an aperture with a diameter D_(a) of approximately2.0″, that is constructively occluded by a mask M with a diameter D_(M)of approximately 1.8″ and enhanced by a baffle 30 having a base ofapproximately 0.27″ in diameter and approximately 0.21″ in length, has aradiation intensity profile that is relatively constant for angles of φup to 90 degrees.

Other baffles can be equally effective at increasing the intensity inthe horizon district. For example, FIG. 11 shows a baffle that isincorporated into the mask M by bevelling edges 48 of the mask M. Wherethe mask M has a substantial thickness, the bevelled edges 48effectively can direct light to the horizon district.

Referring to FIG. 8A, an alternative embodiment of the baffle is shown.Also covered with a diffusely-reflective material, a baffle 41 is formedof multiple extended members 42 defining an intersection 43 at theirmidpoints. The members 42 are preferably planar, but they may be curvedor otherwise. The baffle 41 preferably, but not necessarily, definessymmetrical sections S in the occluded arrangement.

The baffle 41 preferably, but not necessarily, has a length 44substantially equal to the diameter of the aperture 22. Alternatively,the length 44 may be longer to extend beyond than aperture 22, or beshorter and shy of reaching the aperture 22. The baffle 41 preferably,but not necessarily, has a height 46 substantially equal to theseparation distance D between the mask M and the aperture 22.Alternatively, the height 46 may be greater or lesser than theseparation distance D. Like the baffle 30, the baffle 41 extends towardthe aperture 22 of the cavity 16 to create a substantially perpendicularsurface 32 relative to the horizon. Consequently, the baffle 41increases the illumination intensity at the horizon district for a moreuniform profile (radiation or response) in the horizon district.

The baffle 41 may be modified as desired to change the profile. Amodified baffle 41′ is shown in FIG. 8B. The baffle 41′ compared to thebaffle 41 has an enlarged core 45 at the intersection 43. Although thecore 45 is illustrated with a circular cross section, the core 45 may bedifferent shapes. The baffle 41′ may also have greater thickness 47 inthe members 42.

To obtain a relatively uniform profile, the arrangement of FIG. 10 usesa mask diameter D_(M) of approximately 1.8″ and an aperture diameterD_(a) of approximately 2.0″, which results in a mask/aperture diameterratio of approximately 0.9 or 90%. A mask/aperture diameter ratio of 0.9provides a relatively uniform response over a relatively large range ofthe angle φ while maintaining an acceptable range of operation. Further,the disk-shaped mask M is spaced away from the aperture 22 byapproximately 0.3 inches, resulting in a mask distance to aperturediameter ratio of approximately 0.2 or 20%.

The arrangement of FIG. 10 may be enclosed in a cover, e.g., dome 38, toprotect the interior components. Moreover, the arrangement of FIG. 10shows the point element 12 being mounted but rather below the mask M andbaffle 41, outside of the cavity 16. Connection wires 40 from the pointelement 12 may be inserted through bores provided in the mask andbaffle.

With the point element 12 facing the aperture 22 from the underside ofthe mask M, “hot spots” that may result from direct angles of radiationor detection into the cavity 16 can be substantially avoided. By“inverting” the point element 12, effects of Fresnel reflection, whichwould otherwise increase the cosine dependence of the arrangementprofile, may also be avoided. Fresnel reflection generally occurswhenever light travels through a surface between two materials havingdifferent indices of refraction, for example, air and glass or silicon.Much like the cosine dependence of the Lambertian surface on the angle φdiscussed above, Fresnel reflection increases with the angle φ, whichdecreases the illumination intensity of light in the horizon district.

The arrangement of FIG. 10 illustrates the concepts used by the system.The head module-H of the system 10 in certain embodiments includes anoccluded and baffled emitter (distributor R) and in other embodiments,an occluded and baffled detector (detector T). Occluded and baffleddistributors and detectors are disclosed, respectively, in U.S.application Ser. No. 08/590,290, filed Jan. 23, 1996, and U.S.application Ser. No. 08/589,105, filed Jan. 23, 1996, both of which areincorporated herein by reference.

An alternative embodiment of an occluded and baffled emitter is shown inFIGS. 27A and 27B. An elongated lamp L, e.g., a minifluorescent lamp, islocated on the underside 24 of the mask M, between two closely spacedbaffles 41. Electrical power for the lamp is supplied on power leadsthat extend through a passageway formed in the base 18. The height ofthe baffles 41 exceeds that of the lamp L, such that the lamp L is notvisible from the side of the emitter.

In view of the foregoing, it can be seen that constructive occlusion canrender the distributor R and the detector T to provide tailoredradiation and detection profiles. When desired, constructive occlusioncan enhance the operation and function of the distributor R and thedetector T with respect to radiation in the horizon district, or evenrender the distributor R and the detector T to be substantiallyuniformly omnidirectional over a hemispheric area. The profiles of thedistributor R and the detector T can be further enhanced with the aid ofthe baffle. With determinative sizing and positioning of the mask and/orbaffle, the distributor R can be occluded in a manner that enables it todistribute uniform intensity in almost all directions and the detector Tcan be occluded in a manner that enables it to respond uniformly tointensity in almost all directions. The system advantageously appliesthese concepts. However, where the distributor R and the detector T havebeen rendered omnidirectional, the system uses a head module H that is acombination of an omnidirectional device with a partitioned device thatoperates with axial resolution.

In order to obtain directional (or angular) data in tracking areflector, the system employs a head module H that includes at least apartitioned distributor PR with a nonpartitioned detector T, or at leasta partitioned detector PT with a nonpartitioned distributor R, where thepartitioned devices operate with resolution about at least one axis. Inparticular, the system enables the generation and/or detection ofintensity variations between different sections that are indicative of adirection along which the reflector RR1 is positioned. As a feature ofthe present invention, the partitioned devices function and operate in amanner that allows the system to remain relatively simple electronicallyand structurally, and inexpensive.

Generally speaking, where a radiation or detection surface LS as shownin FIGS. 3A and 3B is utilized in the head module H, without the cavity16, the baffle 41 effectively divides or partitions the surface LSand/or a region between the mask M and the surface LS into sections inrendering a directional distributor or directional detector. In thisregard, as explained below in further detail, the light source providingthe radiation surface LS (or the detector providing the detectionsurface LS) is then configured to enable distinct radiation from (ordistinguish between distinct incidental radiation on) each of thesections created by the baffle 41.

Where the radiation surface or detection surface is provided by thecavity 16 and the aperture 22, such as in the distributor R and detectorT described above, the baffle 41 is modified or extended a baffle 51 todivide or partition the region into the sections that are now inclusiveof a volume substantially between the cavity 16 and the mask M. In orderthat the partitioned distributor (or detector) be able to enabledistinct radiation from (or distinguish between distinct incidentalradiation on) each of the sections, the point element 12 is replaced bya plurality of point elements, each of which is associated with adistinct section.

As shown in FIG. 9, the baffle 51 is similar to the baffle 41 of FIG.8A, but with the addition of dividers 53 which are substantiallyextended portions of the planar members 42. The dividers 53 areconfigured such that when the baffle 51 is placed between the mask M andthe cavity 16 (both represented by broken lines), the members 42 remainabove the aperture 22 while the dividers 53 extend below the apertureinto the cavity 16 and approach or abut the interior surface of thecavity 16. For example, where the cavity 16 is hemispherical orspherical, the dividers 53 have an curved profile 55.

Where the radiation or detection surface LS is present, a region Gbetween the surface LS and the mask M is divided by the baffle 41 intosections Si. Where the cavity 16 with the aperture 22 are utilized toprovide the surface LS, a region or volume G′ between the cavity 16 andthe mask M is divided by the baffle 51 into the sections or subvolumesS_(i).

In one embodiment, the baffle 41 and 51 are substantially opaque, havinga thickness of approximately 3.0 mm. In an alternative embodiment, thebaffles 41 and 51 need not necessarily be opaque, provided that theysubstantially divide the region G into the sections, such that lightentering into each section substantially remains within that sectiononly.

Where the baffle 41 or 51 partitions or divides the region into foursections S_(A), S_(B), S_(C) and S_(D), the partitioned device hasresolution about two axes. Two axes of resolution can also be enabledwithin the system 10 where the baffle 41 or 51 partitions the regioninto three sections; however, it is believed that the calculations usedby the system to provide directional information would be more complex.Two axes of resolution are also enabled where baffle 41 or 51 dividesthe region into five or more sections. If only one axis of resolution isdesired, the baffle 41 or 51 is configured to partition the region intofewer sections, for example, two sections.

Where the baffle 51 provides four sections or quadrants (for resolutionabout two axes), an X/Y coordinate system may be superimposed on thebaffle 51, as illustrated, such that the cavity 16 is quartered inaccordance with the azimuth angle ρ being measured from the positive Xaxis. For purposes of better understanding this discussion, individualsections S_(A), S_(B), S_(C) and S_(D) may be defined as follows:

0<ρ<90=section B

90<ρ<180=section A

180<ρ<270=section D

270<ρ<360=section C

While the baffles 30, 41 and 51 all serve to increase the illuminationintensity at the horizon district (i.e., φ=90 or so), the extendedbaffle 51 divides the cavity 16 and renders the distributor R and thedetector T into partitioned distributor and detector PR and PT so thatthey provide resolution or distinguish direction about the X and Y axes.In particular, it is the baffle 51 which enables the partitioned devicesPR and PT to generate intensity variations in a manner that allows thesystem to ascertain at least directional data, if not positional datafor a reflector.

FIGS. 12A and 12B illustrate a partitioned device that is representativeof the partitioned distributor PR and the partitioned detector PT, usingthe cavity 16, the mask M and the baffle 51. The baffle 51 creates thesections, which includes lower sections below the aperture 22 within thecavity 16 and upper sections above the aperture 22 and below the mask M.As mentioned, a plurality of point elements 59 are used instead of thesingle point element 12 of FIG. 10 and each point element 59 isassociated with a distinct section. Each point element 59 may be mountedin a distinct section, in particular, a distinct upper section, on theunderside 24 of the mask M for the reasons previously discussed. Again,the point element 59 may represent light-conveying devices, as describedearlier.

Referring to FIG. 13, the system in one embodiment provides a headmodule H that includes a partitioned detector PT and distributor R. Thepartitioned detector PT may be configured as illustrated in FIGS. 12Aand 12B, and the distributor R may be configured as illustrated in FIG.10. As explained, each point sensor 59 of the partitioned detector PT isconfigured to generate electrical signals based on the light intensitydetected in the respective section. Where the point sensor 59 is aphotodiode, the photodiode has a relatively small responsive area ofapproximately 0.8 square millimeters and a noise equivalent power (NEP)of approximately 6×10⁻¹⁵ Watts/(Hertz)^(0.5). A photodiode with a smallresponsive area has two significant advantages: (i) it generally has lownoise characteristics; and (ii) the greater efficiency of the system(i.e., a decrease in the ratio of sensor size to cavity size meansgreater sensitivity). Using these photodiodes, the partitioned lightdetector's efficiency nears its asymptotic state with a cavity havingapproximately a 1.0 inch diameter or width.

As shown in FIG. 13, intensity variations detected by each of the pointsensors in the partitioned detector PT of the head module H is processedby a processor 49 (a representative circuit 67 thereof being shown indetail in FIG. 15) for display on an oscilloscope 64. The circuit 67 isequivalent to the circuit suggested by a manufacturer of photodiodes,namely, United Detector Technologies (UDT) Sensors, Inc., of Hawthorne,Calif., for use with its quad-cell photodiodes. Others circuits (analogor digital) may be used.

Referring specifically to FIG. 12B, the sections S_(A) S_(B) S_(C) andS_(D) created by the baffle 51 are arranged clockwise, when viewing downon the partitioned detector PT (see FIG. 13). Note that this arrangementcoincides with the sections shown in a conceptual representation in FIG.14, in that the normal extends outwardly from the horizon (or X/Y) planeinto the hemispheric area over the partitioned detector T.

Referring specifically to FIG. 15, the cathodes of the photodiodes areall connected to a common ground terminal. The anodes of the respectivephotodiodes are each connected to the respective current-to-voltageamplifier 50. The voltages are then summed and/or subtracted by one ofthree amplifiers 52, 54 and 57. The first amplifier 52 outputs a signalwhich is the sum of the signals from all four sections S_(A), S_(B),S_(C) and S_(D). The second amplifier 54 sums the signals from thesections B and C, and subtracts the sum of the signals from sections Aand D. The second amplifier's output signal is then divided by the firstamplifier's output signal by a divider 58 that provides and X outputsignal. A third amplifier 57 sums the signals from the sections A and B,and subtracts the sum of the signals from the sections C and D. Thethird amplifier's output signal is then divided by the first amplifier'soutput signal by a divider 60 that provides a Y output signal. Asuitable divider is the DIV100 manufactured and sold by Burr-Brown® ofTucson, Ariz.

The relationship between the X and Y output signals and the sectionsignals is given by the following formulas:

X=[(B+C)−(A+D)]/(A+B+C+D)  Eqn. 1

Y=[(A+B)−(C+D)]/(A+B+C+D)  Eqn. 2

It is understood by one of ordinary skill in the art that Equations 1and 2 may be varied so long as the configuration of the sections S_(A),S_(B), S_(C) and S_(D) is consistent therewith.

The X and Y output signals are fed to the oscilloscope 64 (FIG. 13). TheX output signal is connected to the display's horizontal sweep inputterminal and the Y output signal is connected to the oscilloscope'svertical sweep input terminal. It is understood by one of ordinary skillin the art that the signals X and Y are not necessarily defined within aCartesian coordinate system. A spot 66 on the oscilloscope 64 indicatesthe azimuth ρ and elevation φ position of the reflector. For example,the spot 64 indicated on the oscilloscope 64 is representative of aretro reflector positioned relative to the partitioned detector PT at anazimuth of about 45 degrees and an elevation of about 45 degrees. As thereflector changes elevation, the radial distance of the spot 66 from thecenter of the oscilloscope 64 changes. As the reflector movesazimuthally about the head module H, the spot 66 will trace a path aboutthe center of the oscilloscope 64.

A grid conceptually representative of the coordinate system for the Xand Y output signals is illustrated in FIG. 14. The azimuth (ρ) angle,taking into account the appropriate section (with the appropriatelydefined positive or negative values) for the reflector RR1 can becalculated from the X and Y output signals using the following formula:

ρ=tan⁻¹(Y/X)  Eqn. 3

The elevation φ is related to the radial distance or length L from thecenter of the oscilloscope 64 to the spot 66 (FIG. 13). This radialdistance L is calculated from the X and Y output signals using thefollowing formula:

L=(X²+Y²)^(½)  Eqn. 4

The actual elevation associated with the calculated azimuth ρ and radiallength L is a complex function of the detector geometry. Accordingly, alook-up table given in Appendix A is used to correlate the azimuth ρ andthe length L, to the elevation, as follows. Note, however, that thetable provides the elevation angle in terms of Θ where Θ=90−φ.

Θ={ρ,L; Table}  Eqn. 5

FIG. 14 illustrates conceptually the relationship set forth in AppendixA between the azimuth ρ, the radial length L, and the elevation Θ of aretro reflector detected at the azimuth angle ρ=30. In particular, ifthe reflector is at an elevation of Θ=10 (i.e., near the horizon), thespot 64 will be approximately 0.89 unit length L from the center of theoscilloscope 64. If the reflector moves to an elevation of Θ=80, thespot 64 will appear to closer to the center, with a reduced unit lengthL of approximately 0.76 from the center. Note that so long as the retroreflector remains at an azimuth of ρ=30, the spot will also remain at anazimuth of ρ=30 on the oscilloscope 64, changing only the length L fromthe center to reflect the change in elevation angle. If the retroreflector moves through different azimuths while remaining at the sameelevation, the spot 66 will travel on a somewhat rectangular path aroundthe center of the oscilloscope 64. Accordingly, the system using thetable in Appendix A provides a set of directional data (i.e., ρ, Θ) fora reflector being tracked.

It bears emphasis that the algorithm used in Appendix A is merely one ofnumerous algorithms that may be used by the system. The algorithm ofAppendix A is also one of many algorithms that allows the spot 66 toremain on the display regardless of the position of the object in thedetection zone Z. Moreover, it is understood by one of ordinary skill inthe art that directional data may provided by the system 10 through theuse of analytic relationships (e.g., polynomial equations), as opposedto the described embodiment using the look-up table of Appendix A.

In view of the foregoing, it can be seen that the partitioned lightdetector PT of the present invention provides at least directionalinformation in the form of a set of azimuth and elevation coordinates(ρ, Θ) for a given retro reflector. A partitioned detector embodyingfeatures of the present invention is disclosed in U.S. application Ser.No. 08/589,104, filed Jan. 23, 1996, which is incorporated herein byreference.

As an alternative embodiment of the partitioned devices in general, twopartitioned devices PD₁ and PD₂ (either both distributors or bothdetectors) may be placed back-to-back as shown in FIG. 28, to providespherical coverage that results from the two opposing hemispheric areaof the two devices.

While the embodiment described above uses a head module having apartitioned detector with a nonpartitioned, omnidirectional distributor,the system may also use a partitioned detector with other conventionallight sources under different conditions. For example, an ordinary broadband light bulb can be used where the detection zone is free from othertypes of illumination. Fluorescent light sources that flicker can alsobe used. A suitable fluorescent light bulb is the “Mini Fluorescent”(TM), Model BF659 in white color, made by JKL Components Corp. ofPacoima, Calif. Although conventional light sources will likely providea nonuniform radiation profile in the detection zone Z (the profilebeing particularly deficient at angles of φ at or near the horizonrelative to the light source), the system will function adequately forthose areas substantially normal to and outside the horizon district ofthe light source. The use of the distributor R instead of an ordinarylight source expands the operative zone of the system into a hemisphericarea over the distributor R, including the horizon district of thedistributor R.

In order to track multiple retro reflectors RR_(i) simultaneously withthe foregoing embodiment (see FIG. 1), that is, to provide additionalsets of directional data (ρ_(i), Θ_(i)) for additional retro reflectors(whether affixed to additional objects, or to different locations on thesame object), the system necessarily distinguishes between signalsattributable to distinct retro reflectors. In this regard, it is notedthat the term “simultaneously” is used figuratively, and not necessarilyliterally, in that processing of data for multiple reflectors by thesystem may occur serially and not in parallel. Parallel processing maybe accomplished with additional processors.

The system 10 distinguishes between multiple reflectors by usingspectrally-selective sensors. In particular, where the light emittedfrom the distributor R is broad band light, reflectors of differentspectral characteristics are provided, along with a corresponding set ofspectrally-responsive point sensors (e.g., photodiodes equipped withspectrally-selective filters) for each additional reflector beingtracked. With the corresponding set of point sensors tracking its“assigned” retro reflector, the system is capable of tracking multipleretro reflectors and distinguishing between the intensities variationscollected for different reflectors.

Referring to FIG. 17, multiple sets of spectrally-selective pointsensors 71 and 72 (with frequencies responses of λ₁ and λ₂,respectively) may all be housed in a single partitioned detector PT. Inparticular, the sets 71 and 72 may be arranged such that each sectionbelow the mask M is occupied by one sensor from a given set. Thepartitioned detector PT of FIG. 17 can therefore detect at least tworeflectors with frequency spectrums similar to λ₁ and λ₂. The reflectorsmay each be affixed to different objects, or the reflectors may all beaffixed to a single (substantially rigid) object to track itsorientation.

In general, it is noted that the frequencies or spectral characteristicsof the electronics described herein are not specific wavelengths, butrather denote ranges of wavelengths. The responses from the sensor sets71 and 72 are used in Equations herein to determine the position of thecorresponding reflectors. In general, the spectral characteristics ofthe reflectors need not be identical to the response characteristic ofits “assigned” sensors, though performance of the system 10 is improvedif they have similar characteristics.

If a third reflector is to be tracked, a third set of correspondingspectrally-responsive sensors with frequency spectrum λ₄ may be added tothe partitioned detector PT of the head module H. In the alternative, anadditional head module H_(n) with simply a partitioned detector PT_(n)may be added and used in conjunction with the head module H withoutrequiring reconfiguration of the latter. It can be seen in general thatadditional sets of sensors for detecting additional reflectors may behoused in the partitioned detector of an existing head module, or inseparate and distinct partitioned detectors T_(i). As shown in FIGS. 22Aand 22B, four separate and distinct partitioned detectors PT_(A),PT_(B), PT_(C) and PT_(D) are conveniently mounted on a single platformP, where each partitioned detector houses one set of sensor sets S_(A),S_(B), S_(C) and S_(D).

It has been noted that a single partitioned detector PT of the abovedescription can provide one set of directional data (ρ₁, Θ₁) for a givenreflector. Referring back to FIG. 1, where it is desirable to ascertainthe position of a reflector in three dimensions (along three axes), thesystem uses at least one additional partitioned light detector PT₂ toprovide a second set of directional coordinates ρ₂ and Θ₂, which whenprocessed with the first directional coordinates ρ₂ and Θ₂, provides allthree coordinates for the reflector. The relative positions of thepartitioned detectors PT and PT₂ to each other is made known to thesystem so that it can cross-reference the signals from both partitioneddetectors to ascertain all three coordinates for a reflector from twosets of directional data.

In view of the foregoing, it can be seen that to ascertain all sixcoordinates for an object (that is, position and rotationalorientation), the system uses at least three reflectors and twopartitioned detectors. However, detection of all six degrees of movementof an object is not always desirable or required, and the system 10 canbe configured appropriately.

Referring to FIG. 1, where a second partitioned detector PT₂ is used, itis part of a second head module H₂ providing a second distributor R₂.The second distributor R₂ provides the light that is detected by thesecond partitioned detector. With the two head modules H₁ and H₂ andtheir relative positions known, the system can cross-reference therespective sets of directional data for any one reflector tracking themovement of that reflector in three coordinates. A divider or aseparating wall (not shown) may be situated between the head modules H₁and H₂ to prevent interference by the respective light distributors.Alternatively, the radiation from the respective distributors may bepulsed or flickered at different frequencies, e.g., 100 Hz and 130 Hz.

As shown in FIG. 1, broad band light is emitted throughout the detectionzone Z. Where the detection zone Z contains extraneous objects such asfurniture or walls with extensive reflective surfaces, light isreflected not only off the reflectors, but off these surfaces as well.Any light detected by the head module not attributable to the reflectorcontributes to the background energy which may significantly limit theperformance of the system 10. However, because this background energy(also known as background or self illumination) is not a noise source,but a background source, its effects can be compensated. Where multiplesensors of different spectral responsiveness are used, this backgroundsource can be reduced if not eliminated.

Referring back to the embodiment shown in FIGS. 17A and 17B, multiplesensors of different spectral responsiveness are used, that is, sensorsets 71 and 72 responsive to frequencies λ₁ and λ₂ are used to track twocorresponding reflectors, as previously described. To compensate forbackground illumination, a third set of sensors 73 is provided. Thefrequency response of the third set 73 is selected to be responsive toall wavelengths in the area of the spectrum near the frequencies λ₁ andλ₂ so that it can act as a background nulling detector. To demonstratethe effects of background illumination, responses r₁ and r₂ of the firstand second sets of sensors, after subtraction of the background energy,are given by:

r=K⁻¹R  Eqn. 6

Where: ${R = \begin{pmatrix}r_{1} \\r_{2} \\\vdots \\r_{n}\end{pmatrix}};{K = \begin{pmatrix}1 & K_{12} & \cdots & K_{1n} \\K_{21} & 1 & \quad & \quad \\\vdots & \quad & ⋰ & \quad \\K_{n1} & \quad & \quad & 1\end{pmatrix}};{R = \begin{pmatrix}R_{1} \\R_{2} \\\vdots \\R_{n}\end{pmatrix}}$

And R₁ is the sensor response before background correction and K_(ii)are constants of correction.

As the background level increases, the dynamic range requirements of theelectronics increase. To calculate the magnitude of the selfillumination, integrating sphere models are used. The background light Breflecting off the walls of a room back to the partitioned detector PTis given by: $\begin{matrix}{B = {\frac{A_{e}}{A_{w}}*\frac{W_{r}}{\left( {1 - {W_{r}\left( \frac{A_{e}}{1 - A_{w}} \right)}} \right)}}} & \text{Eqn. 7}\end{matrix}$

Where A_(e) is the acceptance area or aperture of the partitioneddetector PT, A_(w) is the area of the room walls, and W_(r) is the roomwall reflectance.

The signal from the retro reflector is given by:

S=Lr*Pr  Eqn. 8

Where:${L_{r} = \frac{A_{r}}{2\pi \quad D_{r}}};{\Pr = \frac{A_{e}}{\pi \quad T_{r}}};{T_{r} = {D_{r}\tan \quad \left( \frac{\Theta^{\prime}}{2} \right)}}$

and Θ′ is the divergent angle of the retro reflector, as previouslydefined, A_(r) is the area of the retro reflector, and D_(r) is thedistance to the retro reflector.

Table 1 below lists signal to background and A/D requirements forselected conditions using a 1″ diameter retro reflector, where Rs is theroom size in feet, D_(r) is distance to the retro reflector in feet, andW_(r) is the wall reflectance. A smaller signal to background required alarger Analog to Digital (A/D) converter. For a system requiring a 1°resolution, a 20 bit A/D is sufficient or a signal to background of0.013. 20 bit A/Ds are readily available and inexpensive.

Condition Required Signal Background S/B Rs D_(r) W_(r) in Watts inWatts Ratio A/D 12′ 12′ 75% 2.9E-6 2.2E-4 1.3E-2 20 bit 12′  6′ 75%4.6E-5 2.2E-4 2.1E-1 14 bit 12′  6′ 95% 4.6E-5 1.4E-3 3.3E-2 18 bit 12′10′ 10% 2.0E-6 8.1E-6 3.5E-1 14 bit 24′ 24′ 75% 1.8E-7 5.5E-5 3.3E-3 24bit 24′ 12′ 75% 2.9E-6 5.5E-5 5.3E-2 18 bit 24′ 12′ 95% 2.9E-6 3.5E-48.7E-3 18 bit 24′ 24′ 10% 1.8E-7 2.0E-6 8.9E-2 16 bit

A head module H including a partitioned detector PT and a nonpartitioneddistributor R is shown in FIG. 16. The partitioned detector PT and thedistributor R of this head module each has its own cavity. A cavity 16_(R), mask M_(R) and baffle 41 are provided for the distributor R, and aseparate cavity 16 _(PT), mask M_(PT) and baffle 51 are provided for thepartitioned detector PT, albeit the cavity 16 _(R) is actuallyconfigured in the mask M_(PT) of the partitioned detector PT. Configuredin this manner, the partitioned detector PT and the distributor Rfunction without significant disturbance to the other. The distributor Rdistributes light into the hemispheric area over the head module H,including the horizon district around the distributor R (and the headmodule H). Any light reflected by a reflector in the hemispheric area isdetected by the partitioned detector PT, even if reflected from thehorizon district. Equipped with the extended baffle 51, the partitioneddetector PT is able to detect intensity variations between the sectionsto enable the system to provide a set of directional data of ρ and Θ foreach reflector.

The head module with separate cavities may be the simplest and leastcostly to manufacture. The separate cavity feature enables the use ofcontinuous or slowly oscillating illumination and relatively largerlight sources. This embodiment is advantageous in that it avoids the useof moving components and imposes relatively slow response requirementson the electronics of the system.

As a variation on the head module, reference is made to FIGS. 18A and18B. A single cavity 16 is provided and shared by a distributor R and apartitioned detector PT. One mask M and one extended baffle 51 are usedin this embodiment. The partitioned detector PT uses three sets ofsensors 71, 72 and 73 to detect two reflectors (the third set 73 forbackground illumination). Since the distributor R shares a cavity 16that has been divided by the baffle 51, the distributor R uses aplurality of emitters 74, one for each section under the mask M. As afurther variation on the head module, the emitters 74 can be broad bandpulse emitters. By measuring the time elapsed for the pulses to returnto the head module H, the system can obtain a range R of the reflectorfrom the head module H, by: $\begin{matrix}{{Range} = \frac{Time}{2c}} & \text{Eqn. 9}\end{matrix}$

where c is the speed of light=3.998×10⁸ m/sec.

A pulse leading edge width or rise time of approximately 1 nanosecondwould give a resolution of approximately 0.15 m or 5.8″. As opposed torequiring an electronics response time of approximately milliseconds(10⁻³ sec) as in the separate cavity embodiment discussed above, thisembodiment typically requires an electronics response time ofapproximately nanoseconds (10⁻⁹ sec). With the elapsed time measurementproviding actual range data (as opposed to the representative length Ldiscussed above), the system using this variation of the head module isable to provide all three coordinates of a reflector without using asecond head module. In order to track rotational movement, the system 10needs only two additional retro reflectors, both of which are alsotracked by the head module H. It is understood by one of ordinary skillin the art that the “time of flight” variation is not limited to thesingle-cavity embodiment, but may also be used in the separate-cavityembodiment, described earlier.

While background illumination can be contending factor in theembodiments described above, the system can be configured to generateminimal background illumination, as discussed below.

Referring to FIGS. 19A and 19B, the light distributor R of the headmodule H is replaced by a scanning light mechanism 76. The scanninglight mechanism 76 includes a plurality of scanning mirrors 78 whosemovement are guided by galvanometers 80. Light from a point light source82 is redirected by the mirrors 78 to form a scan beam 84 that sweepsthe zone Z. Other types of optical scanners exist, such as rotatingwedges and rotating reflectors, and may be used in the system.

The scanning beam 84 may be approximately 10 degrees wide. The beam orits sweeping action is not timed or sequenced, but simply serves toilluminate a limited section or portion of the detection zone Z at agiven time. The partitioned detector PT is set with a detectionthreshold such that no position tracking is attempted by the system 10if the beam strikes no reflector. When the beam 84 does illuminate areflector, the optical intensity striking the partitioned detector PTexceeds the threshold and the system 10 processes the intensityvariations detected by the sets of sensors.

The partitioned detector PT of this embodiment is split into symmetricalcomponents. As shown in FIG. 19B, the partitioned light detector PT isdivided into two portions PT_(a) and PT_(b), between which the scanningmechanism 76 is positioned. By splitting the partitioned detector PT,shadowing by the scanning mechanism 76 is significantly reduced and thepartitioned detector PT remains capable of detecting radiation about twoaxes of resolution. The head module H of this embodiment provides only aone set of directional data (azimuth and elevation) for a reflector.

Because the scan beam 84 illuminates only a section of the zone Z at agiven time, this embodiment has a distinct advantage of lower backgroundillumination and may thus be preferred for applications with a largenumber of reflectors. Without the need to perform backgroundsubtraction, the system of this embodiment can readily track multipleretro reflectors using a small number of filter sensor combinationswhich cooperatively perform a “color” analysis on the signals detected.In fact, the system can be configured to distinguish between a verylarge number (i.e. thousands) of spectrally-distinguishable reflectors,using as little as two or three sets of sensors. Of course, it isunderstood by one of ordinary skill in the art that a larger number ofsets can be used.

The color analysis performed by the system is much like that used by thehuman eye to detect color. The eye using only three detectors (or“cones”) is able to distinguish between a variety of colors.Correspondingly, the system using only three sets ofspectrally-selective sensors 91, 92 and 93 as shown in FIG. 19B, candistinguish between a variety of spectrally-distinguishable reflectors.

If the scan beam 84 happens to strike multiple reflectorssimultaneously, the system can process the signals in a manner much likethat used for compensating background illumination, described above.

The system also uses color analysis in another embodiment. Referring toFIGS. 20A and 20B, the system 10 includes a head module H having anonpartitioned detector T and a partitioned distributor PR, withseparate cavities 16 _(T) and 16 _(PR), separate masks M_(T) and M_(PR),a baffle 41 and a cavity dividing baffle 51. The partitioned distributorPR is equipped with different color lamps C_(A), C_(B), C_(D) and C_(D)to radiate a different color (i.e., radiation of a different wavelength)from each section. The resulting color mix reflected by a reflector isdetected by the detector T using three single point sensors 95. Thesystem analyzes the color mix detected by the detector T to obtain a setof directional data (azimuth and elevation) for that reflector.

Additional reflectors may be tracked where the reflectors are equippedwith shutters, such as LCD shutters. This allows this embodiment of thesystem 10 to distinguish between multiple points, e.g., by timing theshutters so that the light data transmitted by each reflector istransmitted as pulse data at different pulse rates.

Still referring to FIGS. 20A and 20B, the partitioned distributor PR inan alternative embodiment may be equipped with emitters of differenttemporal frequency. That is, each section of the partitioned distributorPR may house a lamp or emitter that flickers at a distinct frequency sothat the nonpartitioned detector T is able to distinguish between lightfrom each lamp or emitter.

While the above embodiments of the present invention are configured asoptically-passive'systems, the invention may also be configured as anoptically-active system. Referring to FIG. 21, active light sources 88 ₁and 88 ₂, such as LEDs, replace the optically-passive reflectors(thereby obviating the use of a light source or light distributors).With one partitioned detector PT₁, directional data for each of thesources 88 ₁ and 88 ₂ is obtained. With two partitioned detectors PT₁and PT₂, positional data in all three coordinates for both of sources 88₁ and 88 ₂ obtained. The active light sources are distinguishable fromeach other by emitting distinguishable colors, or oscillating atdistinguishable frequencies.

As another optically-active embodiment of the present invention, thesystem 10 includes the partitioned distributor PR of FIG. 20B, and thepartitioned detector PT of FIG. 17. The partitioned distributor PR withthe color lamps C_(A), C_(B), C_(D) and C_(D), or emitters of differenttemporal frequencies, as described above, may itself be mounted on orotherwise attached to the object being tracked. The resulting color mixfrom the partitioned distributor PR is detected by the sets of sensors71, 72 and 73 of the partitioned detector PT of FIG. 17, which nowperform a color analysis on the color mix to provide a set ofdirectional data for the object relative to the partitioned detector PT.

It is noted that the accuracy of the directional performance of thelight distributor and/or light detector can be empirically optimizedusing a variety of parameters. For example, the height, relativediameter, thickness, and reflectivity of the mask, the width andreflectivity of the shoulders, the height and reflectivity of the baffleassembly, the shape and reflectivity of the cavity, and the photodiode'sdiameter, all affect the light detector's directional response.Conversely, the distributor's and/or the detector's directionalperformance can be tailored to be nonuniform, if desired, by varyingspecific parameters. For example, decreasing the distance between themask and the aperture will decrease the spherical profile of thedetector's response, while increasing the detector's “on-axis”efficiency. When the mask is placed in the plane of the aperture, thedetector's “on-axis” efficiency improves to about 90%, compared to about40% with a mask above the aperture, but its response profile isnarrowed, rendering a less uniform detection profile. The lightdetector's spectral response can also be tailored by using spectrallyselective paint on the diffusely reflective surfaces or a filtered domeor cover.

Referring back to FIG. 1, for all the embodiments discussed above, thesignals representative of the position of the object tracked can beconverted into video signals to drive a video monitor displaying theposition or movement of the object. The reflectors may be removablyaffixed to the object, such that they can be readily transferred betweendifferent game equipment, such as game swords or game boxing gloves.

As further embodiments of the system, an occluded distributor ordetector 98 may be configured to provide to a radiation or detectionprofile that is substantially uniform over a spherical area. Asillustrated in FIGS. 23A, 23B, 23C, the occluded device includes atubular member 100 having a diffusely reflective interior surface 102defining an interior volume or cavity 104. The tubular member 100 isillustrated with a cylindrical configuration; however, the member 100need not have a circular cross section. The tubular member 100 has openends 106 providing two apertures 108 from which radiation may enter intoor exit from the cavity 104. The apertures 108 are constructivelyoccluded with masks M and the cavity 104 is divided by a planar baffle110 to form two half volumes V₁ and V₂ inside the tubular member 100. Apoint element 112 is housed in each half volume, at a midlocation alongthe length of the member 100. Accordingly, the device 98 is operationalwith respect to one axis of resolution.

Where the point element 112 is an emitter, radiation is emitted fromeach end 106 of the occluded device 98 with a tailored distributionprofile over the aperture 108. Correspondingly, where the point element112 is a detector, the occluded device 98 detects radiation with atailored detection profile over the aperture 108.

For substantially spherical coverage, a second occluded tubular device114 is provided. The second device 114 is structured similarly to thefirst device 98 and thus like numerals refer to like elements. Thesecond device 114 is positioned orthogonally to the device such that itsapertures 108 are offset substantially 90 degrees from the apertures 108of the first device. As the device 114 is also divided by the planarbaffle 110, the two devices together are operational with respect to twoaxes of resolution.

Additionally, the concept of constructed occlusion can be accomplishedby reconfiguring the substantially Lambertian surface into multipledistinct surfaces which can alternatively occlude each other. Asillustrated in FIGS. 24A-24D, an annular or ring structure 120 isillustrated, having an opening or otherwise nonoptical area 122 throughwhich an axis or boresight 124 can be drawn. It is understood by one ofordinary skill in the art that the area 122 may alternatively benon-reflective and/or nontransmissive. The axis 124 is substantiallynormal to a plane within which the ring structure 120 is confined. Theelevation angle φ is defined as the angle from the boresight 124.

The ring structure 120 provides two distinct surfaces that can eitherradiate or detect light. In particular, the ring structure 120 includesa first annular structure 126 that provides a first surface 128 thatfaces inwardly toward the area 122. The ring structure 120 also includesa second annular structure 130 (shown in exploded view in broken linesin FIG. 24A) that provides a second surface 132. The second structure130 fits within the first structure 126 and may reside at anypredetermined depth within the first structure 126 as shown by the arrow123. Fitted inside the first structure 16, the second structure 130effectively projects angularly from the first structure 126 with thesurfaces 128 and 132 being angularly offset from each other. In oneembodiment, the first and second surfaces are normal to each other, withthe second surface 132 being substantially parallel with the plane ofthe area 122 and thus substantially normal to the boresight 124. Whilethis may offer the simplest configuration, the first and second surfaces128 and 132 need not be normal to each other so long as they can occludeeach other as desired and any angle therebetween is known. Typicallymutual selective occlusion is afforded if the structures 126 and 130 arenonparallel. Moreover, the second surface 132 need not be normal to theboresight 124 so long as any angle therebetween is known.

Referring to FIG. 24C, the second structure 130 is situated at a lowerdepth within the first structure 126. However, as mentioned, the secondstructure 130 can also be situated at a midline of the first structure126, as shown in FIGS. 25A-25C. Depending on dimensions 134 of the firststructure 126 and 136 of the second structure 130, and a spacing 137 thefirst and second structures, the cross section K can be keptsubstantially constant for most angles of φ. It can be seen that for theangle of φ approaching the horizon as shown in FIG. 24C, the first andsecond left surfaces 128 _(L) and 130 _(L) are unoccluded, whereas thefirst and second right surfaces are occluded, to provide the total crosssection K. Where the angle of φ is substantially zero, only the secondsurfaces 130 _(R) and 130 _(L) are unoccluded, whereas both the firstsurfaces 128 _(R) and 128 _(L) are effectively occluded to provide thetotal cross section K.

Accordingly, the first and second structures 126 and 130 eachconstructively occludes the surfaces of the other for different anglesof φ, keeping the cross section area K relatively constant to provide arelatively uniform radiation or detection profile. Like the occludeddevices described earlier, the ring structure 120 is substantiallyomnidirectional for either radiation purposes or detection purposes.Where the second structure 130 is at a mid-depth in the first structure126, the cross section K also remains relatively constant for differentangles of φ. As shown in FIG. 25C, the left second structure 130 _(L)constructively occludes or masks a portion 138 of the left first surface128 _(L), while the right first structure 126 _(R) completely occludesthe right second surface 132 _(R). Accordingly, the first and secondstructures 126 and 130 each constructively occludes the surfaces of theother for different angles of φ, keeping the cross section area Krelatively constant to provide a relatively uniform radiation ordetection profile. In FIGS. 24A-24C and 25A-25C, the structure 120 isconfigured as a circular ring; however, it can be configured in anyshape, provided the opening or nonoptical area 122 is present.

Referring to FIGS. 25A-25C only, to provide at least one axis ofresolution in rendering the structure 120 directional in one coordinate,the structure 120 is divided into at least two discrete portions orsegments 150. The disclosed structure 120 of is divided into foursegments 150 a, 150 b, 150 c and 150 d, as best shown in FIG. 24B, toprovide two axes of resolution rendering the structure 120 directionalin two coordinates, in the manner described earlier.

In FIG. 25A, the segment 150 d is shown partially broken away to revealthe cross section view of segment 150 a which is representative of allthe segments 150 a-150 d. The division in the structure 120 ispreferably, but not necessarily, made so that each segment providessubstantially symmetrical and equal surfaces 128 and 132. In thisembodiment, the segments 150 a-150 d are insulated from each other bygaps 152 filled with air or insulating material such that each segmentis unaffected by the radiation or detection function of the others.

With the structure 120 as a radiator or emitter, each of the segmentscan radiate distinguishable radiation. With the structure 120 as adetector, the structure 120 is electrically configured such that eachsegment 150 a-150 d can generate signals representative of the radiationincident on the respective segment.

As a further variation, the structure 120 can be constructed out ofsilica, or a calorimetric substance that is sensitive to infraredradiation. In that regard, the first and second surfaces 128 and 132 maybe rendered a dark shade or color such that infrared radiation incidenton the structure 120 is readily detected.

Where spherical coverage is desired or appropriate, two ring structures120′ and 120″ may be used in a back-to-back configuration as shown inFIGS. 29A and 29B. In the illustrated embodiment, a singlenon-reflective and non-transmissive member 122′ is provided between thetwo structures 120′ and 120″ and each of the structures 120′ and 120″ isdivided into the segments 150 a′-150 d′ and 150 a″-150 d″, respectively,to provide resolution about two axes (the segments 150 d′ and 150 d″ arenot shown and the segments 150 c′ and 150 c″ are shown partially brokenaway).

In the orientation of FIGS. 29A and 29B, it can be seen that the ringstructure 120′ provides “top” hemispherical coverage and the ringstructure 120″ provides “bottom” hemispherical coverage, which togetherprovide the spherical coverage.

Referring to FIGS. 26A and 26B, another embodiment of a constructivelyoccluded, directional optical device 160 is illustrated. The device 160includes a base 162 constructed much like the base 18 earlier described,except that the base 162 contains four spherical cavities 164 a, 164 b,164 c and 164 d, all of which are constructively occluded by a mask 166configured from an upper portion 168 of the base 162. Each of thespherical cavities has a surface or aperture 167 that is occluded by themask 166 so that the cross section area K remains substantially constantfor most angles of φ. A plurality of optical point elements 180, eitheremitters or detectors, are provided, with each being associated with adistinct cavity.

Described another way, it can be seen that the four spherical cavities164 a-164 d jointly form a larger cavity (delineated in FIG. 26B bybroken line segments 169) which has been partitioned by a core section170 of the base situated between the four spherical cavities, on whichthe mask M is supported. The core section 170 acts much like the baffle51 described earlier in enabling the radiation in each cavity 164 a-164d to remain therein. With the four spherical cavities, the device offerstwo axes of resolution, as described earlier.

As mentioned, the radiation or detection profile of an occluded devicein accordance with a feature of the present invention can be tailored asdesired or needed. As an example of an occluded device providing anonuniform, tailored radiation or detection profile, reference is madeto FIGS. 30A-30C. An occluded device 200 is shown, having a diffuselyreflective cavity 202, which in the illustrated embodiment, iscylindrical with a constant circular cross-section area 204. An aperture206 of the cavity 202 provides a radiation or detection surface 208. Theoccluded device 200 includes a diffusely reflective mask M.

In this embodiment, the mask M has a width W_(M) that is greater than awidth W_(A) of the aperture 206 and is positioned a distance D from thesurface 208 or aperture 206. For example, the width W_(M) may beapproximately 0.265″, the width W_(A) may be approximately 0.250″, andthe distance D may be 0.075″. In this embodiment, the mask M overreachesand extends beyond the aperture 206. With the mask M so configured, itcan be seen that a cross section area K_(H) for angles of φ in thehorizon district is substantially at a maximum, and is reduced to across section area K_(E) as the angle φ is reduced. In fact, for anglesof φ approaching zero (i.e., normal to the aperture 206), the crosssection K is zero, as the mask M completely occludes the aperture 206.Accordingly, the device 200 has reduced function in the elevation anglesover the hemispheric area or sector which the device 200 H-faces. Butbecause the cross section area K_(H) is substantially at a maximum andremains substantially at the maximum for all azimuth angles (i.e.,0<ρ<360), the device 200 is rendered an azimuthal device having aradiation or detection profile that is substantially uniform in theazimuth direction at or near the horizon district of the device 200.

To provide resolution about at least one axis in the azimuth direction,the device includes a diffusely reflective baffle 214 that partitions ordivides the cavity 202 into the sections S. Referring specifically toembodiment of FIG. 30B, the baffle 214 preferably, but not necessarily,divides the cavity 202 into four section S_(A) S_(B), S_(C) and S_(D).As an emitter, the device 200 may then include four emitters 220_(A)-220 _(D), each of which is housed in a distinct section. Much likethe hemispherical partitioned distributor PT of FIGS. 20A and 20B,described earlier, the emitters 220 can be lamps of different colors ordifferent temporal frequencies, except that the device 200 operatesazimuthally, as opposed to hemispherically.

As a detector, the azimuthal device 200 may include a plurality ofdetectors (also represented by reference numerals 220) in associationwith the sectors. For the device 200 to locate the azimuthal angle ofincoming light over 360 degrees in its horizon district, the baffle 214is configured to partition the cavity 202 into at least the foursections S_(A), S_(B), S_(C) and S_(D), each of which houses a distinctemitter 220.

For the azimuthal device 200 to locate the azimuth angle of incominglight over 180 degrees in its horizon district, the baffle 214 isconfigured to partition the cavity 202 into at least three sections thatspan preferably, but not necessarily, 270 degrees. As shown in FIG. 30C,the three sections may be sections S_(A), S_(D) and S_(C), each with itsrespective detector 220. As a fourth detector 220 is not used in thisembodiment for detection coverage of 180 degrees, the “nonactive”section S_(B) is shown without a detector.

It is understood by one of ordinary skill in the art that the pluralityof sections and/or the plurality of optical elements 220 associated withthe sections S may be tailored or changed to meet the desired functionand operation of the device 200 as either a partitioned azimuthaldistributor or a partitioned azimuthal detector.

As a further example of tailoring the radiation or detection profile ofthe azimuthal device 200, the device 200 is shown in FIGS. 31A-31C wherethe width W_(M) of the mask M is substantially equal to the width W_(A)of the aperture 206. It can be seen that the cross section area K_(H)has remained substantially unchanged from that of FIGS. 30A-30C;however, cross section area K_(E)′ of FIG. 31A has increased over thearea K_(E) of FIG. 30A.

It is noted that the optical elements 220 of FIGS. 30A-30C arepositioned in the “bottom” of the cavity 202, whereas the opticalelements 220 of FIGS. 31A-31C are positioned on the “sides” of thecavity 202. In either instance, the sites of the elements 220 within thecavity 202 are selected so as to avoid “hot spots,” as describedearlier, if “hot spots” are undesirable or disruptive. The embodiment ofFIGS. 30A-30C may be preferred for a floor-mounted azimuthal device andthe embodiment of FIGS. 31A-31C may be preferred for a wall-mountedazimuthal device.

Like the embodiments described above, the cavity 202, the mask M, and/orthe baffle 214 may be diffusely reflective, and the cavity 202 may beany shape, although the cylindrical shape is preferred in mostinstances. A protective cover 224 may also be provided.

It can be seen that the present invention provides a relatively simpleand cost effective system that can track the position of objects movingin a three-dimensional zone, without a large number of optical elementsor complex processing electronics. Although the foregoing discloses thepresently preferred embodiments of the present invention, it isunderstood that the those skilled in the art may make various changes tothe preferred embodiments shown and described without departing from thescope of the invention. Accordingly, the invention is defined only bythe following claims.

We claim:
 1. A position tracking system, comprising: a radiant energydetecting transducer; a radiant energy emitting transducer for causingradiant energy to be directed from an object to be tracked toward thedetecting transducer; and a processing circuit coupled to the detectingtransducer, for processing at least one received-energy responsivesignal produced by the detecting transducer to determine the position ofthe object to be tracked, wherein one of the transducers comprises: (a)a base having a diffuse active optical area which faces substantiallytoward at least a portion of an intended field of operation of the onetransducer; (b) a mask spaced from the base and positioned to occlude aportion of the active optical area of the base with respect to theportion of the intended field of operation, the mask having a reflectivesurface facing substantially toward the portion of the active opticalarea of the base; (c) a diffusely reflective cavity formed in one of theactive optical area of the base and the reflective surface of the mask;and (d) an electromagnetic transducer for transducing between radiantenergy associated with the active optical area and correspondingelectrical signals.
 2. A position tracking system as in claim 1, whereinthe radiant energy emitting transducer is adapted for mounting in closeassociation with the object to be tracked.
 3. A position tracking systemas in claim 1, wherein the radiant energy emitting transducer comprisesa radiant energy source, and a radiant energy reflector adapted formounting in close association with the object to be tracked.
 4. Aposition tracking system as in claim 3, wherein the radiant energysource comprises the base, the mask, the cavity and the electromagnetictransducer.
 5. A position tracking system as in claim 1, wherein thedetecting transducer comprises the base, the mask, the cavity and theelectromagnetic transducer.
 6. A position tracking system as in claim 5,wherein: the detecting transducer further comprises a baffle locatedbetween the mask and the base for optically dividing the active opticalarea into a plurality of regions; and the electromagnetic transducercomprises a plurality of radiant energy detectors, each opticallycoupled to a corresponding one of the regions, for transducing betweenradiant energy associated with the corresponding region of the activeoptical area and electrical signals.
 7. A position tracking system as inclaim 1, wherein: the emitting transducer comprises the base, the mask,the cavity and the electromagnetic transducer; the emitting transducerfurther comprises a baffle located between the mask and the base foroptically dividing the active optical area into a plurality of regions;and the electromagnetic transducer comprises a plurality of radiantenergy emitters, each optically coupled to a corresponding one of theregions, for emitting radiant energy into the corresponding region ofthe active optical area in response to electrical signals.
 8. A positiontracking system as in claim 1, wherein the emitting transducer comprisesa source of substantially continuous broad band radiant energy.
 9. Aposition tracking system as in claim 1, wherein the emitting transducercomprises a pulse source of broad band radiant energy.
 10. A positiontracking system as in claim 1, wherein the mask and an aperture of thecavity are arranged so as to tailor a predetermined performancecharacteristic of the one transducer over an operative field of the onetransducer.
 11. A position tracking system as in claim 10, wherein thetailored performance characteristic provides a substantially uniformperformance of the one transducer over a range of angles with respect tothe one transducer.
 12. A position tracking system as in claim 10,wherein the tailored performance characteristic provides a substantiallynon-uniform performance of the one transducer over a range of angleswith respect to the one transducer.
 13. A position tracking system as inclaim 12, wherein the substantially non-uniform performance of the onetransducer provides an increase in efficiency in regions on or about anaxis of the one transducer.
 14. A position tracking system as in claim12, wherein the one transducer is the radiant energy detectingtransducer.
 15. A position tracking system as in claim 1, wherein: theradiant energy emitting transducer comprises a plurality ofelectromagnetic transducers for transducing from electrical signals tocorresponding radiant energy signals; and each of the electromagnetictransducers emits radiant energy signals having a difference in apredetermined characteristic from radiant energy signals emitted fromthe others of the electromagnetic transducers.
 16. A position trackingsystem as in claim 15, wherein the radiant energy signals emitted fromthe electromagnetic transducers comprise light, and the difference inthe predetermined characteristic comprises a difference in color orwavelengths.
 17. A position tracking system as in claim 15, wherein thedifference in the predetermined characteristic comprises a difference ina pulsing rate.
 18. A position tracking system as in claim 15, whereinthe difference in the predetermined characteristic comprises adifference in temporal frequency.
 19. A position tracking system,comprising: a radiant energy detecting transducer; a radiant energyemitting transducer for causing radiant energy to be directed from anobject to be tracked toward the detecting transducer; and a processingcircuit coupled to the detecting transducer, for processing at least onereceived-energy responsive signal produced by the detecting transducerto determine the position of the object to be tracked, wherein one ofthe transducers comprises: (a) a base having a diffuse active opticalarea which faces substantially toward at least a portion of an intendedfield of operation of the one transducer; (b) a mask having a reflectivesurface spaced from the base and positioned to occlude a portion of theactive optical area of the base with respect to the portion of theintended field of operation; and (c) an electromagnetic transducer fortransducing between radiant energy associated with the active opticalarea and corresponding electrical signals.
 20. A position trackingsystem as in claim 19, wherein the emitting transducer comprises asource of substantially continuous broad band radiant energy.
 21. Aposition tracking system as in claim 19, wherein the emitting transducercomprises a pulse source of broad band radiant energy.
 22. A positiontracking system as in claim 19, wherein the mask and the active opticalarea of the base are arranged so as to tailor a predeterminedperformance characteristic of the one transducer over a operative fieldof the one transducer.
 23. A position tracking system as in claim 22,wherein the tailored performance characteristic provides a substantiallyuniform performance of the one transducer over a range of angles withrespect to the one transducer.
 24. A position tracking system as inclaim 22, wherein the tailored performance characteristic provides asubstantially non-uniform performance of the one transducer over a rangeof angles with respect to the one transducer.
 25. A position trackingsystem as in claim 24, wherein the substantially non-uniform performanceof the one transducer provides an increase in efficiency in regions onor about an axis of the one transducer.
 26. A position tracking systemas in claim 24, wherein the one transducer is the radiant energydetecting transducer.
 27. A position tracking system as in claim 19,wherein: the radiant energy emitting transducer comprises a plurality ofelectromagnetic transducers for transducing from electrical signals tocorresponding radiant energy signals; and each of the electromagnetictransducers emits radiant energy signals having a difference in apredetermined characteristic from radiant energy signals emitted fromthe others of the electromagnetic transducers.
 28. A position trackingsystem as in claim 27, wherein the radiant energy signals emitted fromthe electromagnetic transducers comprise light, and the difference inthe predetermined characteristic comprises a difference in color orwavelengths.
 29. A position tracking system as in claim 27, wherein thedifference in the predetermined characteristic comprises a difference ina pulsing rate.
 30. A position tracking system as in claim 27, whereinthe difference in the predetermined characteristic comprises adifference in temporal frequency.
 31. A position tracking system,comprising: a light detector comprising: 1) a detection surface, 2) amask positioned a predetermined distance from the detection surface, 3)a baffle that divides a region between said detection surface and saidmask into sections, and 4) a plurality of sensors, each associated witha distinct one of the sections; and a plurality light sources forcausing light to be directed from one or more objects to be trackedtoward the light detector, wherein each of the light sources emits lighthaving a difference in a predetermined characteristic from light emittedfrom the others of the sources.
 32. A position tracking system as inclaim 31, wherein the difference in the predetermined characteristiccomprises a difference in color or wavelengths of light.
 33. A positiontracking system as in claim 31, wherein the difference in thepredetermined characteristic comprises a difference in pulsing rate. 34.A position tracking system as in claim 31, wherein the difference in thepredetermined characteristic comprises a difference in temporalfrequency.
 35. A position tracking system as in claim 31, wherein theone transducer further comprises a diffusely reflective cavity formed inthe detection surface of the mask.
 36. A position tracking system,comprising: a radiant energy detecting transducer; a radiant energyemitting transducer for causing radiant energy to be directed from anobject to be tracked toward the detecting transducer; and a processingcircuit coupled to the detecting transducer, for processing at least onereceived-energy responsive signal produced by the detecting transducerto determine the position of the object to be tracked, wherein one ofthe transducers comprises: (a) a base having an optical area which facessubstantially toward at least a portion of an intended field ofoperation of the one transducer; (b) a mask having a reflective surfacespaced from the base and positioned to occlude a portion of the opticalarea of the base with respect to the portion of the intended field ofoperation, wherein the mask and the optical area of the base areconfigured to tailor a predetermined performance characteristic of theone transducer over an operative field of the one transducer (c) abaffle located between the mask and the base for dividing a regionbetween the reflective surface of the mask and the optical area of thebase into a plurality of sections; and (d) a plurality ofelectromagnetic transducers for transducing between radiant energy andcorresponding electrical signals, at least one of the electromagnetictransducers being coupled to each of the sections.
 37. A positiontracking system as in claim 36, wherein said one transducer furthercomprises a diffusely reflective cavity formed in one of the opticalarea of the base and the reflective surface of the mask.
 38. A positiontracking system as in claim 37, wherein: an aperture of the cavity formsthe optical area of the base; and the baffle extends between theaperture and the reflective surface of the mask.
 39. A position trackingsystem as in claim 37, wherein: an aperture of the cavity forms theoptical area of the base; and the baffle extends from the reflectivesurface of the mask through the aperture of the cavity.
 40. A positiontracking system as in claim 39, wherein the baffle extends tosubstantially abut an interior surface of the cavity.